A chocolate bar a day can cut the risk of heart disease and stroke by as much
as 39 per cent, according to scientists.

Cocoa beans contain flavanols, which are thought to increase nitric oxide in the blood and improve the function of blood vessels.

For the same reason, the experts found, dark chocolate is more beneficial than milk or white chocolate due to higher levels of antioxidants and cocoa.

The eight-year study, of nearly 30,000 people aged 35 to 65, confirmed the results of previous, smaller studies into the health benefits of cocoa products.

Brian Buijsse, a nutritional epidemiologist at the German Institute of Human Nutrition, Nuthetal, Germany, who co-authored the subsequent report, found that even one square of chocolate can be beneficial.

But if the dose is increased by just six grams, there were 85 fewer heart attacks and strokes per 10,000 people.